How to create a hotkey to press a button?

I have a POS software which doesn't support hotkey to press a certain button. I have to press this button very often and having always to use mouse is slow and uncomfortable.
I tried to use AutoHotKey or AutoIt to emulate the mouse click. However, the problem is that AutoHotKey and AutoIt couldn't locate the button. This button control seems to be an internal object of the POS software and not visible to AutoHotKey and AutoIt.
Any suggestions? Thanks!

Place the window in the top-left corner of your screen. Record a macro that moves the pointer all the way to the top left corner of your monitor, then down to the button and clicks it. Then you can run your macro however often you like, because no matter where your mouse pointer is, it will zoom up to the top left corner, then down to the button.